The invention is based on a fuel injection pump as defined hereinafter. In a fuel injection pump of this type, known from German Offenlegungsschrift DE-OS 2 246 056, in which a pump piston defines a pump work chamber with its face end and is moved axially in a cylinder lining, the control edge that, by overtaking a control opening disposed in a cylinder wall, controls the injection onset and that is located on the face end of the pump piston in the rotary position region of the pump piston, which region controls the rated load range of the engine to be supplied, is slanted toward the control opening in such a way that the injection onset in this region is shifted to a later onset. Besides enabling optimization of the injection onset for the high-load range, this makes possible a high maximal combustion pressure in the pump work chamber in the other operating points as well, since these can now be adapted independently of the rated load range.
Consequently, the known fuel injection pump allows an increase of the maximal combustion pressure over the entire operating range of the fuel injection pump, without exceeding the maximal permissible limit value for the mechanical loading capacity of the parts, primarily in the rated load range.
In the design of the known fuel injection pump for emissions-optimized internal combustion engines, however, the injection onsets must be delayed so late that, when the engine is cold, in the lowest load range, or at zero load, white smoke is emitted, which raises the pollutant emission of the engine to be supplied when it is in this state.
In order, however, to be able to shift the injection onsets to an early enough time for an optimal and low-polluting combustion even for a "cold start", a fuel injection pump is known from a German patent application Serial No. P 42258030, which at this point in time is not published and which corresponds with U.S. Pat. No. 5,396,871 in which the control edge on the face end of the pump piston that controls the supply onset is divided into two regions separated by a longitudinal groove, of which one region, which is disposed in the partial-load zone, makes possible a very early supply onset, while the second region has a control edge offset toward the "late" direction and in which a further indentation is disposed, which forms a third control edge with which a further delay of the supply onset is possible in the range of large fuel supply quantities, so that with this fuel injection pump, an optimal adaptation of the supply onset to the different operating ranges can be achieved, even in a "cold start" of the engine.
This last aforementioned fuel injection pump has the disadvantage, however, that by means of the longitudinal groove, which serves as a stop groove between the control edge regions and which divides the very early supply onset region from the total control path region, the usable control path at the pump piston remaining for "normal operation", that is apart from a cold start, is narrowed so that the fuel injection system is no longer accurately controllable in all operating ranges. This narrowing of the usable control path leads to marked "partial supply quantity dropoffs"; that is, a very narrow control path of the control rod, which continues on the pump piston as the torsional path, causes sudden major changes in supply quantity. These sudden fluctuations in supply quantity, as they occur in the known fuel injection pump, primarily at the transition region between the very early supply onset and the stop groove, cause a fluctuation in engine speed, which can lead to self-reinforcement of the fluctuation in the entire system and thus to the familiar "seesaw effect" or intermittent racing in the engine.